The growing success in recent years of phytotherapy preparations based on plant extracts has led to research into formulations with a safer, more reproducible unit dosage than the traditional preparations made by infusion.
Of the various formulations proposed, effervescent preparations based on dry plant extracts have encountered the favour of the public because they dissolve easily, generally have a pleasant flavour and are easier to use than solid forms, which are sometimes relatively large and therefore difficult to swallow. However, this type of preparation also presents some drawbacks.
In effervescent preparations in the form of tablets or granulate, the effervescence is caused by the carbon dioxide generated by the reaction between an acid (usually citric or tartaric acid) and sodium or potassium bicarbonate. The effervescence sometimes develops in a very violent way, causing excessively rapid hydration of the dry plant extracts contained in the tablet or granule, and leading to the formation of a layer of highly concentrated solution which prevents the water from reaching the innermost part of the tablet or granule, thus delaying and sometimes even preventing complete dissolution of the preparation.
Another problem closely connected with effervescence, and consequently with excessively violent hydration, is the formation of a thick layer of froth, which once again slows complete dissolution of the preparation. Plant extracts, which are often rich in saponin, are particularly liable to froth formation.
Another problem with effervescent formulations is their instability in the presence of moisture.
In an attempt to solve these problems, coating the particles of plant extract with oily, waxy or fatty substances (EP-A-911032) or using a surplus of water-soluble medium (EP-A-922450, EP-A-919227) has been proposed. However, these solutions are not wholly satisfactory because they involve formulation difficulties associated with coating techniques and the use of large amounts of excipients.